Enhanced visual and audible signaling for sensed alarm condition

ABSTRACT

A sensor alarm which provides an alarm notification of a dangerous condition within a monitored space, further provides notice of its current state condition, from among several states, with distinct message comprising a combination of encoded audible and visible mnemonics annunciations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of the commonlyowned, copending U.S. provisional patent application entitled EnhancedVisual and Audible Signaling for Smoke Alarm Condition, Ser. No.60/135,877, filed May 25, 1999 by William P. Tanguay.

In addition, some of the material disclosed and claimed in thisapplication is also disclosed in a commonly owned, copending utilityapplication entitled Multi-station Dangerous Condition Alarm SystemIncorporating Alarm and Chirp Origination Feature, Ser. No. 09/318,698,filed May 25, 1999 by T. J. O'Donnell.

TECHNICAL FIELD

This invention relates to the field of safety alarms, and moreparticularly to alarms for detecting the presence of a dangerouscondition in a monitored space.

BACKGROUND ART

As known, there are several different types of safety type alarms,including smoke alarms, heat alarms, and carbon monoxide detectoralarms. While each of these differ in the alarm condition they detect,they all perform common alarm signaling protocols to give notice of thedetected condition. The alarm notice is provided locally to warnoccupants within or near the space, and may be provided to a remotemonitoring location by electronic communication. To ensure adequatelocal notice to those in or near the monitored space, the local alarm isprovided with audible and visible annunciation, using horns and lamps.Depending on the type condition being detected, the alarm protocolsdiffer in their excitation pattern and frequency. They may also differin their audible tones and in the intensity of their visible warning.

In locations where there are more than one installed alarm, such as in amulti-room residence where alarms may be installed in each of severalfloors, as well as in each of several spaces on a floor, it is wellknown to functionally interconnect the smoke alarms in a network toallow all units to annunciate an alarm condition detected by any one ofthe networked units. This provides broadcast notice of the alarm toevery occupant, no matter where they are within the residence orbuilding. One characteristic of this networked arrangement, however, isthat it is not possible to determine which of the interconnected unitsdetected the condition and originated the alarm after the alarmcondition has concluded. It is advantageous to know which of severalunits is the originating unit, especially in the event of a false alarmcondition, where it is desirable to replace only the defective unit,which will minimize replacement unit cost and needless time spent forthe services of a contractor or electrician. Without an ability todetermine which of the units originated the false alarm, all units mustbe replaced.

U.S. Pat. No. 5,933,078, by T. J. O'Donnell, issued Aug. 3, 1999, solvedthis problem for common residential applications by providing a smokealarm unit that latches the unit's visual alarm annunciator in the “on”,or illuminated state, whenever the unit detects an alarm condition. Thisoccurs only within the unit which detects the alarm condition. All ofthe other networked units annunciate the alarm, but when the alarmcondition is cleared only the originating unit continues to display avisible alarm state. This allows for immediate identification of thealarm originating unit within the network, and for its replacement inthe event of a false alarm.

One problem with this self identifying unit is that the visual indicatoris constantly lighted in this latched state. Ideally, the buildingoccupant would notice this signal in a relatively timely manner, butoftentimes the condition of smoke alarms, unless sounding their audiblealarm, go unnoticed. Since this condition is capable of accelerating thedischarge of the battery of a battery powered unit, or the back-upbattery of AC/DC model smoke alarms which use the back-up battery topower the visual indicator, its use may be limited to smoke alarms whichare AC powered. To broaden the use of this feature to battery poweredsmoke alarms it is necessary to develop a method of providing theorigination function in a manner which decreases the service life of thebattery by only a small amount.

DISCLOSURE OF INVENTION

The object of the present invention is to provide improved methods andapparatus for displaying the alarm origination feature in a smoke alarm,in a manner which minimizes the load current drawn from the smoke alarmpower source. Another object of the present invention is to provideimproved visual notice of an alarm origination condition to an observer.Still another object of the present invention is to provide a useful andnon-ambiguous hybrid signal when a combination of notice of alarmorigination and low-battery signal is present.

According to one aspect of the present invention, the visualannunciation of an alarm origination condition is provided by pulsedmodulation of the visual annunciator, to produce an intermittent patternof lighted pulses. In further accord with this aspect of the presentinvention, the pulsed width excitation of the visual annunciator is atan average duty cycle which is no greater than approximately 0.075%. Instill further accord with this aspect of the invention, the pulsed widthexcitation of the visual annunciator is at an average duty cycle whichis no less than approximately 0.025%.

According to another aspect of the present invention, the visual patternfor notification of an alarm origination was chosen to broadly emulatethe sequence of three pulses of periodicity of the audible temporalpattern specified by the Underwriter's Laboratories Standard UL217 foralarm annunciation, thereby providing improved recognition of the pulsedvisual alarm origination condition on the basis of its association withthe pattern of the audible annunciation of an actual alarm condition.

In accordance with a still further aspect of the present invention, alow battery annunciation is provided as one of a plurality ofprioritized state conditions of the sensor alarm, with the low batteryannunciation being encoded with a distinct code which allows it to bereadily distinguishable from the other state condition alarms of thesensor alarm.

In the sensor alarm of the present invention a hybrid signalingcondition is defined whereby the visual indicator (LED) uses threesequential flashes to show an alarm origination condition, and theaudible indicator (the horn) “chirps” (if enabled) approximately onceper minute to declare a low-battery condition. Upon relief of eithercondition, the smoke alarm's integrated circuit (IC) functionalspecification requires that the particular indicators return to theirindependent state (either only low-battery condition or only post-alarmcondition).

These and other objects, features, and advantages of the presentinvention will become more apparent in light of the following detaileddescription of a best mode embodiment thereof, as illustrated in theaccompanying Drawing.

BRIEF DESCRIPTION OF DRAWING

FIG. 1, is a schematic diagram of a best mode embodiment of an alarmsensor according to the present invention;

FIG. 2, is a schematic diagram of one element of the embodiment of FIG.1;

FIG. 3, is an illustration of the actuation pattern waveforms of theprior art Underwriters Laboratories (UL217) standards for audibleannunciation of a sensed alarm condition, as well as typical visualsignals and the corresponding internal clock used in the description ofthe present invention;

FIG. 4, is an illustration of the actuation pattern waveforms for visualannunciation of the sensed alarm origination according, as provided bythe alarm sensor embodiment of FIG. 1.

FIG. 5, is an illustration of the actuation pattern waveforms foraudible and visual annunciation of a post-alarm condition (FIG. D.) andlow battery condition (FIGS. B. & C.), as provided by the embodiment ofFIG. 1; and

FIG. 6, is a simplified, representative schematic diagram of a portionof the element of FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic diagram of an exemplary embodiment of an alarmsensor 20 according to the present invention. In a best mode embodimentthe sensor 20 has dual electrical power sources, including alternatingcurrent (AC) power received on lines 22, 24 (marked as the high [H] andneutral [N] inputs in FIG. 1), as well as a direct current (DC) battery26. The battery is nominally 9.0 VDC, and in the dual power embodimentit functions as an emergency, or back-up source of power in the event ofthe loss or failure of the AC signal on lines 22, 24.

The high side of the AC signal on line 22 is coupled through a reactivepower supply, comprising parallel combination of resistor 28 andcapacitor 30, and through current limiting resistor 32 to zener diode34. In its reverse biased state the zener diode 34 limits the peakamplitude of the rectified AC signal to approximately 10, and in itsforward biased state the AC signal amplitude is less than one volt. Thisproduces a half wave rectified signal, which is applied across theseries combination of resistor 36 and light emitting diode (LED) 38. TheLED 38, which is a known type, such as the model LTL307G light emittingdiode (a conventional green color T-1¾ LED) manufactured by LiteonOptoelectronics, is thereby illuminated to visually annunciate thepresence of AC power to the sensor. The half wave rectified signal isalso presented through steering diode 40 to the capacitor 42 at node 44.The capacitor 42 filters the ripple component of the half-wave rectifiedreference signal at node 44 to provide the direct current (DC) referencevalue VDD.

The battery 26 is connected through the anode to cathode of steeringdiode 46 to node 44 and to capacitor 48. The diode prevents therectified AC signal source for VDD from inadvertently charging thebattery, but in the event of the loss of AC power the diode becomesforward biased and allows the battery to supply the VDD source signal tothe sensor and circuitry.

The battery 26 is also connected through steering diode 50 and voltagedivider resistor 52 to the “LOW V” input (pin 3) of an applicationspecific integrated circuit (ASIC) 54. The “LOW V” input (pin 3) of ASIC54 is connected through the bottom leg of voltage divider resistor 60 tothe “LED” input pin 5 of ASIC 54. The battery is also connected throughdiode 50 to the series combination of resistor 56 and light emittingdiode (LED) 58. The LED 58 is also a known type, such as the LiteonOptoelectronics LTL307 R, a conventional red color T-1¾ LED.

The other side of the LED 58 is connected to the “LED” control pin 5 ofthe ASIC 54. As known, an ASIC is a custom designed “ApplicationSpecific Integrated Circuit” which incorporates several unambiguousfunctions, thereby reducing the number of required discrete circuitelements, and conserving circuit board area. In the best mode embodimentthe ASIC 54 is manufactured and sold by the model A5363 by ALLEGROSemiconductor, Inc., 115 Northeast Cutoff, Worcester, Mass., 01615. TheASIC 54 is described in greater detail in the circuit diagram of FIG. 2,which is correlated with the ASIC block diagram of FIG. 1 by the I/O pinnumbers and accompanying descriptive labels.

Referring now to FIG. 2, the LED 58 connected at pin 5 of the ASIC 54 isconnected within the ASIC, through a line 62 to a field effecttransistor (FET) 64. When the FET 64 is turned on by a gate signalapplied on line 66 from logic circuitry 68, it provides a current pathfor the LED 58 from pin 5 (LED) to signal ground 70, thereby allowingthe LED to be energized by battery current in a Low Battery VisualAnnunciator Pattern established by the logic circuitry, as described indetail hereinafter with respect to FIG. 5. The LOW V (low battery) pin 3of the ASIC 54 is connected to a voltage divider within the ASIC, inaddition to the external voltage divider comprising resistors 52 and 60detailed in FIG. 1. This internal divider includes resistors 72-74 whichare serially connected through an FET switch 76 between the VDD pin 6and the VSS pin 9, which in the embodiment of FIG. 1 is connected tosignal ground.

With a normal VDD level of approximately 9 VDC the internal resistordivider provides a nominal threshold voltage at the LOW V pin 3 ofapproximately 73% VDD, or slightly greater than 6.6 VDC. When the powersupply voltage VDD of the smoke alarm circuit falls to approximately 7.5VDC, the threshold of the LOW V pin 3 becomes equal to the internalreference of 5.5 VDC, and the low-voltage function of the ASIC 54 isenabled. In the disclosed circuit, the external voltage dividerresistors are used to modify the actual nominal threshold voltage of pin3 to obtain a low-voltage value moderately different than set by theASIC manufacturer. This threshold voltage is applied to thenon-inverting (+) input of comparator 78, which compares this thresholdvalue to a reference value of approximately 5.5 VDC applied to itsinverting (−) input from internal reference zener diode 80.

In the event AC power is lost, the VDD source voltage is provided by thebattery 26. A drop in the battery voltage with time and current loadwill result in a corresponding drop of the threshold voltage at pin 3.When this threshold value drops below the internal approximately 5.5 VDCreference, as described earlier, the comparator 78 changes states andactivates the Low Battery Visual Annunciator Pattern established by thelogic circuitry 68. The logic circuitry replicates the Low BatteryVisual Annunciator Pattern in a modulated gate signal which it provideson line 66 to sequence the actuation of the FET 64 according to theprotocol of the Pattern.

Referring simultaneously to FIGS. 1 and 2, in the disclosed embodimentof the present alarm sensor 20 as a smoke alarm, smoke detection isprovided by a well-known ionization detector 82 (FIG. 1) which reports adetected condition on line 83 to the DETECT pin 15 input to the ASIC 54.The ASIC provides a high-impedance non-inverting buffer to the detectinput on line 83, which is connected to smoke comparator 85. In FIG. 2the detected condition is provided through line 84 to the inverting (−)input of comparator 85, the non-inverting (+) input of which isconnected to the SENSITIVITY input, pin 13 of the ASIC, which is at thejunction of resistors 73, 74 of the series resistor combination 72-74.

The resistor combination provides a SENSITIVITY threshold voltage havinga nominal value of approximately 50% of VDD at pin 13. In the disclosedapplication, external voltage divider resistors shown in FIG. 1 are usedto modify the sensitivity threshold voltage to a value slightlydifferent than 50% VDD, as required for calibration of the smoke sensingthreshold. The presence of a predetermined smoke level in the ionizationchamber 82 causes the output voltage at line 83 to drop a predeterminedamount. The detector sensed alarm condition signal at the DETECT inputis lower in magnitude than the SENSITIVITY threshold value, causing thecomparator 85 to change states and activate the Audible and Visual AlarmAnnunciator pattern established by the logic circuitry 68.

Under an alarm condition, the logic circuitry 68 actuates the audibleand visual alarms concurrently. In the best mode embodiment, the audibleannunciation is provided by a piezoelectric horn 86 (FIG. 1) which isactuated by horn driver circuitry within the ASIC 54. The horn drivercircuitry within the ASIC is shown generally at 87 in FIG. 2. Thepiezoelectric horn is a thin disk of piezoelectric ceramic materialbonded to a slightly larger diameter of stainless steel disk. Thepiezoceramic disc has two discrete electrodes, generally of silver, thatare screened onto its surface. One larger electrode, commonly referredto as the “silver” electrode, is connected to pin 11 of the ASIC 54. Thesecond electrode is the actual stainless steel disk, commonly called“brass” because of a historical reference to the original disk material,connected to pin 10 of the ASIC 54. A second and smaller silverelectrode, commonly referred to as the “feedback” electrode, isconnected to pin 8 of ASIC 54.

When enabled by the logic elements of ASIC 54, internal NAND gates ofhorn driver 90, in conjunction with output inverters shown connected toASIC 54 pins 10 and 11, comprise a two-stage simple relaxation CMOS (anacronym for Complimentary Metal Oxide Semiconductor) oscillator, wellknown in the art. In combination with external passive components,resistors 88, 89 and capacitor 90 connected to pins 8, 10, and 11 ofASIC 54, this oscillator creates out-of-phase square waves, switchingnearly between VDD and VSS (circuit ground) levels, at pins 10 and 11 ofASIC 54. This voltage application to the piezoceramic disk causes it toflex back and forth along an axis perpendicular to the disk surface. Thevoltage from the feedback element, connected through resistor 88 to pin8 of the ASIC 54, is used to synchronize the internal CMOS oscillator tothe disk's natural resonant frequency. The disk's continuous bendingback and forth, in conjunction with a resonant acoustic cavity closelycoupled to the disk, produces the particular sound used for the audiblealarm.

When actuated, the piezoelectric horn provides an audible alarmcomprising a fixed carrier frequency on the order of 3300 Hz, with anapproximate minimum 85 decibel (dB) sound level (as required by allsafety agencies), which is modulated in a temporal (time varying)pattern. In the illustrated smoke alarm embodiment the modulationpattern is that specified for an audible smoke alarm by UnderwritersLaboratories UL 217 standard. This pattern, as shown in FIG. 3,illustration A), by the by waveform 92, has a nominal 4 second cycle 93,each cycle comprising three consecutive half second pulses 94-96, with ahalf second interpulse period, followed by an approximate 1.5 secondpause 98. The audible effect is “tone-pause-tone-pause-tone-long pause.”

As a result of the UL standard, this rhythmic audible sequence isgenerally, if not inherently, understood by the public to be associatedwith a dangerous smoke alarm condition. Similarly, although not shownhere, the UL 217standard specifies a different, distinct audibletemporal pattern for carbon monoxide detectors which consists of anominal 5.0 second cycle of four 0.1 second pulses, with a 0.1 secondinterpulse period (total 0.7 seconds) followed by a pause ofapproximately 4.3 seconds. These distinct patterns are intended toimmediately distinguish the subject state or nature of the sounded alarmto occupants, and with continuing use it is reasonably assumed that theymay become well enough known to the public to provide subliminal warningof the danger they signify.

Simultaneously with audible annunciation of the local alarm condition,the sensor 20 provides visible annunciation by actuating the RED LED 38in a different, visible temporal pattern. The visible local alarmannunciation pattern is shown by the waveform 100 in illustration B) ofFIG. 3, as comprising a continuing series of pulses 102, having anapproximate pulse width 104 of 10 milliseconds and an approximateinterpulse period 106 of 1.0 second. This is the pattern of the gatesignal applied by the logic circuitry 68 (FIG. 2) on line 66 to activate(“turn-on”) the FET switch 64 and ground the LED 38. The LED is thenpulsed on, powered by the battery 26, at the repetition frequency of thedefined visual temporal pattern.

While the temporal patterns themselves are established by the logiccircuitry 66, the timing control of the pulsed waveforms is governed bythe ASIC oscillator and timing circuitry 108 of FIG. 2. The timingcontrol circuitry 108 provides two clock signals, which are referred tohere as a Fast Clock and a Slow Clock. The Fast Clock has a pulserepetition time of approximately 42 milliseconds, and the Slow Clock hasa pulse repetition time which is approximately 40 times greater, or40*42 ms=1.67 seconds. The Fast Clock provides the appropriate timingfor the sensed alarm audible and visible temporal patterns 92, 100 (FIG.3, illustrations A), B)). The Fast Clock signal is shown by waveform 110of FIG. 3, illustration C). The clock pulses 112 have an interpulseperiod 114 of approximately 42 milliseconds.

Referring to FIGS. 1 and 2, the 1.67 second Slow Clock provides the basetiming for the ionization smoker alarm's standby condition and it iscontrolled by a bias resistor 116 connected to pin 7 of the ASIC 54 anda timing capacitor 118 connected to the ASIC at pin 12. The programmabledual-rate timing circuitry portion of the logic circuitry 108 is shownfor reference in highly simplified form as FIG. 6. Referring to FIG. 6,the timing portion includes comparators 120, 122 which provide theiroutputs on lines 124, 126 to the SET S and RESET R inputs of a bistableflip-flop 128. The inverting (−) input of comparator 120 and thenon-inverting (+) input of comparator 122 are connected through line 129to the external timing capacitor 118 at pin 12. The non-inverting (+)input of comparator 120 and the inverting input (−) of comparator 122are connected to different points of a voltage divider networkcomprising series resistors 130-132.

In the absence of a sensed alarm condition, and beginning with aninitial uncharged state for the capacitor 118, a first current source134 charges the capacitor 118 with a relatively constant current valueof approximately 30 micro amps. At initial conditions, a power-up resetcircuit within ASIC 54 sets the bistable flip-flop such that the “Q”output is at a logic low (unasserted) and the “Q NOT” output is at alogic high (asserted). Additionally note that after the initial cycle,this charging current into capacitor 118 provides the approximately 10ms phase of the master clock signal. The comparator 120 compares theincreasing capacitor voltage to a first reference voltage equal to thesum voltage drop across resistors 131, 132, approximately ⅔ VDD. Whenthe capacitor voltage magnitude exceeds that of the first referencevoltage the comparator 120 changes states and shifts the bistable to theSET state, whereby the “Q” output is asserted and the “Q-not” output isunasserted.

During the standby phase of the ionization smoke alarm, or SLOW CLOCKmode, the SET state of the bistable flip-flop, or the state where the“Q” output is asserted, enables current sink 136 which, when actuated,provides the capacitor with a current sink of approximately 181 nanoamps. As the capacitor 118 discharges over an approximate period of 1.66seconds, the discharging capacitor voltage magnitude falls below that ofa second reference voltage equal to the voltage drop across resistor132, approximately ⅓ VDD. This causes the comparator 122 to changestates and place the bistable in the RESET state, which disables thecurrent sink 136 and simultaneously re-enables the current source 134.The capacitor voltage changes from approximately ⅓ VDD to approximately⅔ VDD in 10 seconds. The charge and discharge process of capacitor 118then repeats, causing a voltage waveform of a sawtooth to be generatedat the ASIC 54 pin 12. The charging and discharging time constants,collectively, provide the approximate 1.67 second Slow Clock signal.

In response to a sensed alarm state signal provided by the detector 82to the DETECT (pin 15) input of the ASIC, the alarm signal is logicallyANDED with the Q output of the bistable 128 by gate 138 to provide agate signal on line 140 to a second higher-value current source 142. Thesecond source 142 provides a constant additional current sink ofapproximately 1.194 micro amps which, when added to the approximate 181nano amps of the first source 134, provides a total discharging currentof approximately 9.375 micro amps. This produces an approximate 32millisecond discharging time constant which, together with the 10 secondcharge interval, provides the Fast Clock interpulse interval ofapproximately 42 milliseconds.

While the Fast Clock is required for timing the audible and visiblealarm temporal patterns, the Slow Clock is used to provide the basetiming signal for the non-alarm state, or standby, conditions. The alarmstate condition is the highest priority state of the sensor alarm, andin reporting an alarm state the smoke alarm circuit is in a higherenergy consumption state then it is under non-alarm conditions. This, ofcourse, is the result of the need to sound both the audible alarm hornas well as the visible annunciation of the alarm state by illuminatingthe LED (38, FIG. 1). Energy consumption may not be a concern when thesensor is supplied solely with AC power, but in those instances wherethe AC power is interrupted and the smoke alarm must rely on its batteryback-up, or for those smoke alarms which only have battery power, energyconservation is critical to the ensuring the performance integrity andbattery life of the alarm.

The smoke alarm of the present invention achieves the energy conservingobjectives under non-alarm state condition while providing full range ofservice performance features. These features include annunciation ofeach alarm origination by the sensor unit, so as to permit itsidentification from among a network of interconnected alarms. It alsoprovides annunciation of a low battery condition to alert maintenancepersonnel and occupants of the need to change the battery.

These annunciations are provided in a pulsed, low power consumptionprotocol, which reduces the actuation duty cycle of the annunciator. Thealarm origination annunciation is provided as a visual announcementonly, but in a pulse coded protocol which emulates to a degree the ULstandard protocol for the audible alarm provided for a dangerouscondition. The present post-alarm origination visual annunciationprotocol, therefore, is associative with the actual audible alarmprotocol, just as the origination notice is functionally associativewith detection of an actual smoke condition by the sensor. Thisassociation results in a notice which is more readily understood by theobserver.

The benefit of this cannot be understated. Under circumstances where acombination of the published safety alarm standards, and proactiveenhancements designed to improve the functionality of the smoke alarm tobuilding occupants, requires the alarms to provide an increasing amountof state conditions, including: (i) annunciation of a detected dangerouscondition within the alarm's monitored space, (ii) the broadcastannunciation of an alarm condition detected by another of a network ofalarms, (iii) an alarm origination indication, and (iv) a low batteryannunciation. The alarms must provide these announcements with a singleaudible and a single visible annunciator, and in a manner which readilydistinguishes one state from another.

In addition, several states may exist in a given sensor at the sametime. As an example, a sensor which originates an alarm annunciationmust also provide an alarm origination notice, of which the second statemay occur simultaneously with a low battery condition. Under the UL 217standard the alarm annunciation of a detected dangerous condition takespriority over all other notices, however, the post-alarm originationnotice state and the low battery state may well exist simultaneously. Itis important, therefore, to provide distinct annunciation protocolswhich are distinguishable from each other and also apparent of the statethey are announcing.

The alarm origination annunciation protocol of the present invention isshown in FIG. 4, illustrations A) and B). It comprises a combination ofzero audible annunciation (zero amplitude waveform 146 of illustrationA)) and a pulsed visible annunciation pattern shown by the waveform 148of illustration B). The visible annunciation protocol comprises threeconsecutive pulses 150-152, followed by a pause interval 154. The pulses150-152 have a pulse width 156 of approximately 10 seconds, and aninterpulse period 158 which is substantially equal to two Slow ClockPeriods, or 2×1.67=3.34 seconds. The pattern repeats every 24 Slow ClockPeriods, or approximately 40 seconds, as shown by the first pulse 160 ofthe next succeeding sequence occurring on the 24^(th) Period 162 of theSlow Clock Signal waveform 164 of illustration C).

As may be apparent, the visible alarm origination annunciation patternis similar to the audible annunciation alarm sequence shown by thewaveform 92 of FIG. 3, illustration A). As stated above, this similarsequence (pulse, pause, pulse, pause, pulse, long pause) associates thepost-alarm visual origination pattern with the actual temporal audiblealarm pattern to permit ready identification of the state condition byan observer. It is suggestive of an historical alarm incident. It is ofcourse distinguishable from the actual alarm state by the fact thatthere is no accompanying audible annunciation.

The alarm origination annunciation is activated immediately following asmoke sensing condition. While smoke is being sensed, the local alarmprovides both a visual warning, illustrated in waveform FIG. 3B), and anaudible temporal warning, illustrated in waveform FIG. 3A). Upontermination of the local alarm condition, and assuming that no othersmoke alarm on the interconnected network is also transmitting an alarmsignal via the interconnect connection, the subject smoke alarm returnsto the standby condition, whereby the SLOW CLOCK is operating. At thistime, the audible horn is silent, illustrated in waveform FIG. 4A), butthe visual warning signal, LED 58, blinks with the unique visual patternillustrated in FIG. 4B). The post-alarm origination annunciation can bedeactivated by an operator by depressing the “Push to Test” switch 166(FIG. 1), which resets the logic of the post-alarm latch within thesmoke alarm ASIC 54.

With regard to battery loading resulting from the use of the presentannunciation format, with a 10 mA LED the alarm origination functionconsumes power at the approximate rate of 0.12 mA-hr per day. A typicalcarbon zinc battery has an approximate “rule-of-thumb” capacity of about150 mA-hrs. This is the “base” battery smoke alarm manufacturers use forshipment, although batteries from various manufacturers have varyingcapacities in a non-discharged state. An alkaline battery chemistry,being about four to six times the cost, provides an approximate“rule-of-thumb” capacity of about 500 ma-hrs. Some smoke alarm productis sold with alkaline batteries. A premium lithium chemistry battery,costing approximately twenty times as much as a carbon zinc battery,provides an approximate “rule-of-thumb” capacity of about 1200 A-hrs.

To provide a comparison of the battery power consumption of the presentduty cycled alarm origination annunciation with that provided by aconstant illumination of the visible annunciatior (e.g. LED), assume ared LED 58 that is constantly illuminated in an alarm origination state,and a circuit that is calibrated by choice of resistor 56 value suchthat the current flow through the red LED 58 is approximately 10 mA. In24 hours (one day), the consumption due to the red LED being steadilyilluminated is 240 mA-hrs, which can exceed the total capacity of acarbon zinc battery. Thus, an alarm origination condition, if unnoticedby the occupant, can result in the low-battery signal being developedeasily within one day of initiation.

The normal single “blink” of the red LED 58, shown in FIG. 3B), consumesapproximately 22 mA-hr/yr of the batteries capacity. The alarmorigination visual signal, shown in FIG. 4B), consumes an additionalapproximate 44 mA-hr/yr of battery capacity. Although it is unlikelythat this signal may go unnoticed by the resident or occupant, it is arelatively moderate increase in the power drain presented to the batteryduring normal operation. For instance, in an AC/DC smoke alarm (the mostpopular smoke alarm being installed today), the normal power drain ofthe entire smoke alarm circuitry is supplied by the AC power supply.Only the periodic self-check of the battery capacity, occurring when thered LED 58 is energized once per minute, consumes the battery's energy.As mentioned earlier, the normal battery consumption may beapproximately 22 mA-hr/yr, and the additional energy consumed by thealarm origination visual signal is about 44 mA-hr/yr, resulting in atotal battery drain of about 66 mA-hr/yr. This increased consumption iswell within the yearly energy supply of even the inexpensive carbon zincbattery, and thus will make an insignificant change in the perceivedbattery life. In fact, the carbon zinc battery is known toself-discharge in approximately two years, thus it is reasonable toexpect that a normal battery life in a smoke alarm will be between oneand two years, even in the low-power application of an AC/DC backupsmoke alarm.

In a smoke alarm application whereby only DC smoke alarms are installed,or in the rarer condition whereby AC/DC smoke alarms may be operatingwithout benefit of AC power for an extended period of time, theadditional 44 mA-hr/yr consumption due to the post-alarm visualindicator is still a reasonable energy increase that will notsubstantially limit the life of the battery.

Finally, users are encouraged to test their alarms at a frequency ofonce per week by the owner's manual and engraving on the cover of thesmoke alarms. The National Fire Protection Agency (NFPA), and of course,the media and fire protection officials, suggest that users test theirsmoke alarms at least once per month. This test, simply pressing andholding the “push-to-test” button on the cover of the smoke alarm, wouldreset the post-alarm latch condition whether or not the user noticed thespecific visual pattern of the red LED 58. As a matter of information, atemporal audible alarm signal, energized for four seconds, and with apeak alarm current of approximately 15 mA, has an energy consumption ofonly 0.00625 mA-hrs. One “excuse” why residents do not test their alarmsweekly is that they are concerned about “draining” the battery. However,the actual power drain due to a temporary alarm condition while testingis extremely insignificant compared to the normal background current ofthe circuit.

In addition to power consumption resulting from the duty cycle actuationof the visible annunciator, there is also the effectiveness of thesignaling protocol. It is well known that human stimulus is enhanced byvariation. A steadily illuminated LED will not command the attentionthat would be obtained by a flashing LED. Human senses respond better tomodulated signals—consider, for example, a police car or fire truck withsteadily illuminated lights and a constant tone siren. These do notexist, simply because flashing lights and modulated sirens will muchbetter notify people that a dangerous condition exists. In an identicalmanner, the flashing LED showing post-alarm condition, or the flashingLED that would aid in recognition of the particular unit with alow-battery condition, is much more effectively communicated than asteady state signal for either condition, as well as providing anenhanced battery life for the unit.

Finally, the use of a three-flash pattern for post alarm condition isdesigned to function as a mnemonic for the user, in that users will beaccustomed to a pattern of three audible tones indicate a smokecondition. Certainly any pattern could have been used, but the authorfeels the best pattern is one that minimizes additional battery drainand that effectively communicates the idea of a “alarm condition”,albeitone in the smoke alarm's past history, to the user. This signal is thecombination of three flashes and a period of inactivity, as illustratedmany times within the previous paragraphs.

When a low battery condition is detected by the ASIC (54, FIG. 1), thelow battery annunciation protocol may be initiated, but it cannot beactivated in the presence of either an actual alarm annunciation, ormight be confusing if activated during an alarm originationannunciation. Among the different sensor states, the low batterycondition has the lowest priority. Absent the existence of a higherpriority state, and in the presence of a low battery condition, the ASIClogic circuitry (68, FIG. 1) actuates the low battery annunciation witha combination audible and visible protocol shown in illustrations B) andD). The visible annunciation pattern is similar to, but distinguishablefrom, the alarm origination pattern which is again illustrated in FIG.5, illustration C) for the convenience of comparing the two. Similarly,for convenience, illustration A) shows the Slow Clock signal.

The audible annunciation of the low battery state comprises a singlepulse (audible “horn chirp”) which occurs every 24 Slow Clock Periods,or approximately every 40 seconds. This is shown in illustration FIG. 5illustration B) by the waveform 168, with individual pulses 170, 171occurring in consecutive cycles 174, 175. The pulses 170, 171 have anapproximate 10 millisecond pulse width 176.

The simultaneous visible annunciation of post-alarm and low batterycondition is a pulsed pattern shown by the waveform 178 of illustrationD). The visible annunciation protocol comprises four consecutive pulses180-183, followed by a pause interval 184. The pulses 180-183 have apulse width 186 of approximately 10 seconds, and an interpulse period188 which is substantially equal to two Slow Clock Periods, or2×1.67=3.34 seconds. The pattern repeats every 24 Slow Clock Periods, orapproximately 40 seconds, as shown by the first pulse 190.

The present sensor alarm is capable of both standalone operation indetecting and annunciating a dangerous condition within its ownsmonitored space, as well network operation in which it is connected withother alarms to provide “broadcast” annunciation of an alarm conditiondetected in any one or more of the interconnected sensors. In FIG. 1,the input/output (I/O) pin 2 of the ASIC 54 provides the sensor'sinterface connection to the other sensors. The I/O is connected throughline 192 to the other networked sensor alarm units 194-197, which areshown symbolically as UNIT B-UNIT E. The line 192 includes a low passfilter comprising the series resistor 198 and shunt capacitor 200. Azener diode 202 provides suppression for the interconnecting linetransients.

Although the invention has been shown and described with respect to abest mode embodiment thereof, it should be understood by those skilledin the art that various changes, omissions, and additions may be made tothe form and detail of the disclosed embodiment without departing fromthe spirit and scope of the invention, as recited in the followingclaims.

I claim:
 1. A sensor alarm, for annunciating an alarm condition in response to its detection of a dangerous condition within its installed space, comprising: sensor means, for detecting the presence of a dangerous condition and for providing an alarm signal in response thereto; and alarm means, including an audible annunciator and a visible annunciator, and including logic circuitry having an alarm signal protocol which, in response to the presence of said alarm signal, actuates said audible annunciator and said visible annunciator to provide a combination audible and visible alarm annunciation of the dangerous condition during an alarm interval; as characterized by: said logic circuitry further including an alarm origination signal protocol for providing, in response to the antecedent presence of said alarm signal, and at the conclusion of said alarm interval, pulsed excitation of said visible annunciator to provide an encoded visible annunciation of the sensor alarm as the originating source of the alarm annunciation.
 2. The alarm sensor of claim 1, wherein said alarm protocol actuates said audible annunciator in a fixed, audibly rhythmic pattern, in each of a plurality of succeeding cycles within the alarm interval.
 3. The alarm sensor of claim 2, wherein said fixed, audibly rhythmic pattern is representative of the audible annunciation identified for smoke alarm conditions by Underwriters Laboratories standard UL
 217. 4. The alarm sensor of claim 2, wherein said alarm origination signal protocol provides said encoded visible alarm origination annunciation as periodically varying illumination of said visible annunciator in a manner which emulates the fixed, audibly rhythmic pattern of the audible annunciation of said alarm condition, to provide to an observer an associative identification of said visible alarm origination annunciation with said audible alarm annunciation.
 5. The alarm sensor of claim 4, wherein said visible alarm origination annunciation comprises a fixed, visually rhythmic pattern of pulsed illumination, in each of succeeding cycles within the alarm interval, said visually rhythmic pattern comprising three pulses of illumination within each said cycle.
 6. The alarm sensor of claim 5, wherein said three pulses of illumination occur within the first half of the time period of each said cycle.
 7. The alarm sensor of claim 2, wherein said alarm origination signal protocol provides said encoded visible alarm origination annunciation while inhibiting actuation of said audible annunciator.
 8. The alarm sensor of claim 3, wherein said alarm origination signal protocol provides said encoded visible alarm origination annunciation as a periodically varying illumination of said visible annunciator in a manner which emulates the UL 217 standard for the audible alarm annunciation.
 9. The alarm sensor of claim 5, wherein said visible annunciator is a light emitting diode.
 10. The alarm sensor of claim 1, further comprising: a battery; battery monitoring circuitry detecting the presence of a low battery voltage condition and for providing a low battery signal in response thereto; and wherein said logic circuitry further includes a low battery annunciation signal protocol which, in response to the presence of a low battery signal in the absence, both individually and jointly, of an alarm annunciation and an alarm origination annunciation, actuates said audible annunciator and said visible annunciator, jointly, to provide an encoded combination of audible and visible annunciation of a low battery condition.
 11. The sensor of claim 10, wherein said encoded combination of audible and visible annunciation comprise a pulse encoded audible low battery annunciation and a pulse encoded visible low battery annunciation.
 12. The sensor of claim 10, wherein said pulse encoded audible low battery annunciation and said pulse encoded visible low battery annunciation each comprise periodically repeating patterns of pulses.
 13. The sensor of claim 12, wherein said pulse encoded audible annunciator comprises a horn.
 14. The sensor of claim 13, wherein the periodically repeating pattern of said encoded audible annunciation comprises an emitted horn chirp.
 15. The alarm sensor of claim 12, wherein said pulse encoded visible low battery annunciation comprises a fixed, visually rhythmic pattern of pulsed illumination, in each of succeeding cycles within the alarm interval.
 16. The alarm sensor of claim 12, wherein said visually rhythmic pattern comprises three pulses of illumination within each said cycle.
 17. The alarm sensor of claim 16, wherein said three pulses of illumination occur within the first half of the time period of each said cycle.
 18. A sensor alarm, of the type which originates annunciation of an alarm in response to its detection of a dangerous condition within its monitored space, and which also annunciates an alarm originated by an external sensor alarm to which it is connected for response, comprising: sensor means, for detecting the presence of a dangerous condition and for providing a monitored space alarm signal in response thereto; interconnect means, for receiving external sensor alarm signals from external sensor alarms connected thereto; and alarm means, including an audible annunciator and a visible annunciator, and including logic circuitry having an alarm signal protocol which, in response to the presence, both individually and jointly, of said monitored space alarm signal and said external sensor alarm signal, actuates said audible annunciator and said visible annunciator, jointly, to provide audible and visible alarm annunciation of the dangerous condition during an alarm interval; as characterized by: said logic circuitry further including an alarm origination signal protocol for providing, in response to the antecedent presence of said monitored space alarm signal, and at the conclusion of said alarm interval, pulsed excitation of said visible annunciator to provide an encoded visible annunciation of the sensor alarm as the originating source of the alarm annunciation.
 19. The alarm sensor of claim 18, wherein said alarm protocol actuates said audible annunciator in a fixed, audibly rhythmic pattern, in each of a plurality of succeeding cycles within the alarm interval.
 20. The alarm sensor of claim 19, wherein said fixed, audibly rhythmic pattern is representative of the audible annunciation identified for smoke alarm conditions by Underwriters Laboratories standard UL
 217. 21. The alarm sensor of claim 19, wherein said alarm origination signal protocol provides said encoded visible alarm origination annunciation as periodically varying illumination of said visible annunciator in a manner which emulates the fixed, audibly rhythmic pattern of the audible annunciation of said alarm condition, to provide to an observer an associative identification of said visible alarm origination annunciation with said audible alarm annunciation.
 22. The alarm sensor of claim 21, wherein said visible alarm origination annunciation comprises a fixed, visually rhythmic pattern of pulsed illumination, in each of succeeding cycles within the alarm interval.
 23. The alarm sensor of claim 21, wherein said visually rhythmic pattern comprising three pulses of illumination within each said cycle.
 24. The alarm sensor of claim 23, wherein said three pulses of illumination occur within the first half of the time period of each said cycle.
 25. The alarm sensor of claim 19, wherein said alarm origination signal protocol provides said encoded visible alarm origination annunciation while inhibiting actuation of said audible annunciator.
 26. The alarm sensor of claim 20, wherein said alarm origination signal protocol provides said encoded visible alarm origination annunciation as a periodically varying illumination of said visible annunciator in a manner which emulates the UL 217 standard for the audible alarm annunciation.
 27. The alarm sensor of claim 22, wherein said visible annunciator is a light emitting diode.
 28. The alarm sensor of claim 18, further comprising: a battery; battery monitoring circuitry detecting the presence of a low battery voltage condition and for providing a low battery signal in response thereto; and wherein said logic circuitry further includes a low battery annunciation signal protocol which, in response to the presence of a low battery signal in the absence, both individually and jointly, of an alarm annunciation and an alarm origination annunciation, actuates said audible annunciator and said visible annunciator, jointly, to provide an encoded combination of audible and visible annunciation of a low battery condition.
 29. The sensor of claim 28, wherein said encoded combination of audible and visible annunciation comprise a pulse encoded audible low battery annunciation and a pulse encoded visible low battery annunciation.
 30. The sensor of claim 28, wherein said pulse encoded audible low battery annunciation and said pulse encoded visible low battery annunciation each comprise periodically repeating patterns of pulses.
 31. The sensor of claim 29, wherein said pulse encoded audible annunciator comprises a horn.
 32. The sensor of claim 30, wherein the periodically repeating pattern of said encoded audible annunciation comprises an emitted horn signal.
 33. The alarm sensor of claim 28, wherein said pulse encoded visible low battery annunciation comprises a fixed, visually rhythmic pattern of pulsed illumination, in each of succeeding cycles within the alarm interval.
 34. The alarm sensor of claim 33, said visually rhythmic pattern comprising four pulses of illumination within each said cycle.
 35. The alarm sensor of claim 34, wherein said four pulses of illumination occur within the first half of the time period of each said cycle. 